1. Field of the Invention
The present invention relates in general to improvements in a golf ball.
2. Discussion of the Related Art
There is known a golf ball consisting principally of, for example, a spherical body having a certain degree of elasticity, and a rubber-made cover covering an outer surface of the spherical body. The spherical body includes a rubber-made, spherical core which is wound with a rubber thread or other fiber. In an outer surface of the rubber-made cover, there are formed a multiplicity of shallow recesses or dimples each having, in general, a substantially circular shape whose diameter is about 1–3 mm, such that the dimples are distributed substantially evenly over the entire outer surface of the cover. The dimples assist the ball, when hit by a club, to fly high and straight in a golf course. That is, the dimples serve to increase the flight distance and the directional stability of the ball.
In the following description, the term “golf course” is interpreted to mean a golf course area excluding a putting green, unless otherwise specified.
In general, a putter is used as a club for putting in a green of the golf course. It is considered important, in a putting play, to set a hitting surface of the putter to be perpendicular to a desired direction in which the ball is intended to run, namely, to be perpendicular to a line to a target hole which line is determined on the basis of various factors such as influences of grass grain upon the ball, and to then swing the putter to stroke the ball parallel to the determined line. However, even if the putter is swung or stroked straight and parallel to the determined line, the ball does not necessarily run along the line, resulting in difficulty of making the ball run in the desired direction with a sufficient stability. Such a difficulty of controlling the direction of the ball tends to be increased, particularly, in a putting stroke with what is called a “soft touch”, in which the ball is hit with a comparatively small hitting force.
Various experiments conducted by the present inventors for studying about the above-described problem revealed that dimples formed in the outer surface of the ball make it difficult to putt the ball in the desired direction with a sufficient stability. A pressed area of the outer surface of the ball, which is pressed by a face of a club as the ball is hit by the club, is elastically deformed to become substantially flat, and a reaction force is then generated as a result of the elastic deformation in the pressed area. This reaction force which restores the pressed area to its original shape, i.e., a part-spherical face serves as a thrust force for thrusting or moving the ball. In this instance, strictly speaking, the pressed area does not become entirely flat due to the presence of the dimples, and some protrusions and recesses remain in the pressed area. The thrust force is generated by a comparatively protruding area of the pressed area which is located between the dimples, namely, by a contact area of the pressed area which is actually brought in contact with the club face. The thrust force is not generated by the other area of the pressed area which is not actually brought in contact with the club face.
In a putting stroke, in which the ball is generally hit with a comparatively small hitting force, the above-described pressed area generally has a diameter so small as about 5–15 mm, for example, about 10 mm, so that the dimples each having a diameter of about 1–3 mm are not necessarily distributed evenly within such a small pressed area, unless the dimples and the pressed area are intentionally positioned relative to each other. The uneven distribution of the dimples within the pressed area means that the center of balance of the contact area of the pressed area which is actually brought into contact with the club face, i.e., the center of distribution of the reaction force applied to the club face from the ball deviates from the center of the circular-shaped pressed area, whereby the reaction force does not act in a direction parallel to a direction in which the club is swung or stroked, resulting in difficulty of making the ball run in the desired direction with a sufficient stability.